The present invention relates to a method of and apparatus for determining a physical property of a material and is particularly related to a method of and apparatus for determining a physical property of a material using surface enhanced Raman emissions.
Various methods of and apparatus for determining physical properties of materials are commonly used in connection with hydrocarbon exploration and production activities. Optical fibers, for instance, require no electrical power and are inherently capable of operating at high temperature. Raman scattering within a fiber can be used to measure temperature as a function of position along the fiber and this is the basis of xe2x80x9cdistributed temperature sensorxe2x80x9d systems. These types of systems are described in Fiber Optic Sensors, ed. Eric Udd, John Wiley and Sons NY(1991), incorporated herein by reference. Other types of fiber optic sensors can be constructed by adding mirrors or diffraction gratings to the fiber. But, even with these additions, there are many types of conventional sensors for which no fiber optic equivalent exists.
Another technology for producing sensors is xe2x80x9cmicromachiningxe2x80x9d, and devices produced by this process which involve both mechanical and electrical components are called MEMS (Micro-Electro-Mechanical-Systems). These devices typically have dimensions on the order of 10xe2x88x923 m and smallest features on the order of 10xe2x88x926 m. Typically, these devices require electrical power to operate although some sensors have been produced which are energized optically. Devices that combine optics and micromachining are sometimes called MOEMS (Micro-Opto-Electro-Mechanical-Systems).
For borehole applications, it is often disadvantageous for sensors to require an electrical power source to operate. MOEMS devices may require electrical power to operate in addition to the light provided by the optical fiber. Each such device in the borehole must have a power supply means. If several MOEMS devices are distributed along an optical fiber, separate optical connections are required at each device. Connections are well known to be sources of failure in borehole equipment and having many such connections can make a system unreliable. Finally, each MOEMS device will likely require separate packaging, with ports to allow optical fiber entry and possibly ports to allow fluid entry. Having separate MOEMS packages distributed along the optical fiber will make installation along the well completion time consuming and difficult.
It is an object of the present invention to provide an improved method of and apparatus for determining a physical property of a material, particularly for use in connection with hydrocarbon exploration and production activities.
The present invention relates generally to a method of and apparatus for determining a physical property of a material and more particularly to a method of and apparatus for determining a physical property of a material using surface enhanced Raman emissions. The method includes: attaching nanoparticles to a substrate; positioning the substrate near the material; illuminating the nanoparticles with photons having wavelengths that stimulate surface enhanced Raman emissions; detecting photons emitted as a result of the illumination; and determining the physical property of the material using the detected photons. The apparatus includes: a substrate; nanoparticles attached to the substrate; a light source, connected to the substrate, for illuminating the nanoparticles with photons having wavelengths that stimulate surface enhanced Raman emissions; a photodetector, connected to the substrate, for detecting photons emitted as a result of illumination of the nanoparticles; and a processor, connected to the photodetector, for determining a physical property of material near the nanoparticles from the detected photons. The inventive method and apparatus are particularly adapted for use in connection with hydrocarbon exploration and production activities. The invention and its benefits will be better understood with reference to the detailed description below and the accompanying drawings.